This invention relates to a removable closure for a tubular opening, such as an oil filler tube, comprising a cover part fastened by a bayonet lock to said tubular opening, and a gasket of rubber or rubber-like material for sealing the opening.
It is known to provide a cap for closing a fuel tank with a bayonet lock. The same principle can also be applied to other kinds of tubular openings, such as filler tubes for lubricating oil. Usually the cap has a gasket to assure leak-proof sealing of the opening.
It has been found that particularly in the case of closures which are opened only very rarely, the gasket, which normally consists of rubber, adheres very tightly to the sealing surface of the tubular opening. Even where the gasket is wetted with oil, for example in the case of an oil filler tube, it still sticks to the oil filler tube which may, for example, be formed of plastic material. As a result of the adhesion of these parts to one another, it becomes impossible, or possible only with extreme difficulty, to release the cap, since the adhesion must be overcome by shearing forces applied by turning the cap.
European Patent No. EP 00 20 987 discloses a closure in which a cup-shaped cap is provided whose free inside diameter corresponds to the outside diameter of the opening to which it is to be applied. To close the opening the cup-shaped cap is reduced in diameter by a constricting device which consists of radially acting thrusters that are brought from an initial position to a locked position by rotating a collar. The opening is opened by rotating the collar in the opposite direction, causing the thrusters to return to the initial position and releasing the cap. A disadvantage of this type of closure, however, is that polymer film hinges are necessary for imparting the radial motion to the thrusters, and they can easily be damaged by improper handling. There is also the danger that, at very high and very low ambient temperatures, the operational reliability of the closure may be impaired due to the properties of the plastic.